Detonation meter



R. G. PIETY DETONATION METER Dwz, 195.2

2 sHEETs-SHEET 1 Filed sept. 13, 1948 S E mw mV .Fm Ov EP T v T me A BYl NN. o.

R. G. PIETY DETONATION METER Dec. 2, 1952 2 SHEETS- SHEET 2 Filed Sept. 13. 1948 IIIIIIIIIIIIIIIIIII'IIIL .BY M M INVENTOR 00 R. G. PIETY ATTORNEYS Patented Dec. 2, 1952 UNILIESD" PATENT OFFICE DETONA-TION M-ETEBf Raymond' G2 llety," Bartlesville,' Okla.; assignfor' tol Phillips Petroleum Company; a corporationofiDelaware Application September'lS, 1948, SeriaLNo.- 49,082-1 (Cl. VSL-350"y 2" Claims;

1J This' invention relates to electrcallmeasurementor" physical forces, Yand it has particular relation `tor the measurement; of peak values, andi alternatively of, 'average valiies, of1 .the knockscaused by detonationof'a fuel andlair miic'ture.

in `an internal". combustion engine.

This application is related. to-Y my prior, apT plication Serial-No. 503,166;flledSeptember/ 20,

1943;'vnowPatent No; 2,448,322); and;entitled;v

Detonation Meter!" The'` primary object of` my, invention is, -to.r.e

place or supplement' 'the' .humanear used. in the prior'art to' determine when knocking is.' takingvlvplace by ,a standard electronic device notk suh-` ject' .'t'o human differences. between individuals, nor human. erro'n. by, providing, suitable methods.'-

an'd apparatus.

Another' important object iis to provide ian., electronic..- device which willfnot only. detectv knocking.. but Will` give theV degree of knockiritensity;

Another object is to provide a detonationtmeter that.' will" 'give' thev degree ofY knock intensity as. ai reading ofi, the peak knockintensity duringa short' 'period'.

Another object istoprovide a detonation meter thatxwill' give the degree of knock intensity asan average of, the". knockintensty over a short period- A` further, object" is 'to accomplish the above listed "objects withoutV intro'ducing, any new use. of the variablevhuman ear.

In thelprior artv the testing oifuelslfor knocking was done ina test engine, the knockingbe.-v

ing listened for by ear in conjunctionlwith. olo-Y servations on a cathoderay tube of therate of change, of pressure in the cylinder. This. im-.

portanty test should. not be made relyingV sov much onthe ear due to the impossibility` of standardiz-V Bysubstituting` an` electronic device,y not only is moreY acute ing hearing-,in human beings.

hearing obtained but the` hearing` is.. ab-r solutely.standardizedso thatdilierent individuals running the test, or the same person on different days,A will'-A get. identical .results even .though their. hearing may` varyV greatly from timey to time. .Y 'Ihe human ear. cannot. judge theY absolute in'' tensity` ofknocking., My electronic device can grade the knocking asto degree inan yaccurate manner.

Other objects are to'providemethods andapparatususefullin signalling-y andindicating. Y

Numerous other objects Willbe apparent to factorsinto' the' priorv art" rating of 2 the fuel` but.- merely remove the variations introducedlbyfthe..

thoselskinedin the weapon reading` the accom-.-

panying specification and' 4Vclairns,and studying"r the drawings.

In'the drawings:n Figure 1 is' a schematicl diagram of v"the functional units of an illustrative embodiment ofiny invention, with voltage-time diagrams .of "the currents carriedbywi'res between vthe units shownl near their respective'wire's;

Figure- 2"is an electricalwiringdiagram show'- ingin symbolslthe' wiring ofthe device illustrated: in Figure 1.

Before discussing the detionation o'r"'kn'ock"` meter itselfj'a` brief description' of the' theory'.

oifknockiwillbe `outlined to give .the basis forthe; reasoning' back bofl the' design. Knocking oc# curs when van' explosive gas mixture fforms is ignited anddetona'tes in v'anl engine cylinderardfl large' differences inpres'sure' are'generate'd with? inthe cylinder;V These pressure differences" arepropagated as soundJWaves-'within the 'cylinder and` they are'V reflected back and' frthluntiltneir sure" Aofi the 'gas in "the vcylir'rd'er'is, m'eas'ul"edby.Y somet'ype of 'pressure indicatorfit will be' found; that the "effect `of` these' reflections back.' and i fortlr'within the 'cylinderand also within'tlie" solidwallsis'to select.v out ofthe original exciting pressures short trainsorsuperposedidampedi sine waves; The i requen'cy' 'of oscillation" of each' of` then clampedY sine waves: corresponds' to. one of" the. modes of vibration 'of'l the system:

meterg, I use the'modes` with' 'frequencie'sfb'el tween 12,000 and4r 17,00'0" 'cycles'.A The" ping' which 1 is heard when the engine is knocking is nothing more than. the sound. generated" -bythe excitation of some' 'of these'4 normal. .modes between`12;000f

and' 173000 cycles;

haverath'er highfrequenci'es' ofV oscillation, "and it' turns outthat in "order" to' generate a .pressure variation with 'appreciableenergy' at these fre-n quencies, a Very"`rapi'd'. rise "in pressure' "is 'ref quired." .Tli'elpre'sence of mechanical .oscillations of high"'frequency('several thousand- `cycles` per secondi.l isltherefore'.v an indication of a rapid rise in pressure. in 'the' cylinder: This rapid; rise" ofi. pressure is" also an .indication Vof knocking, an'd it isvthis' rapid pressure change that 'generates` the Voltage in the' pickup 4` of my device,

more rapid the riseof pressure,:the more Violent' the knock andthe greater the' voltage generated by the pickup, so I can thereby determine the degree of knock intensity from the rate of pressure rise.

In spite of the complexity of the relation between the pressure changes in the cylinder and the acoustic and mechanical vibrations set up, it has been observed that the intensity of the knock under controlled conditions can be used to compare one fuel with another.

There are several pressure sensitive devices which are able to transform the pressure variations within an engine cylinder to a corresponding electrical voltage. I have been using a very satisfactory magneto-striction type indicator manufactured by the Standardl Oil Company of California the voltage output of which is substantially proportional to the rate of change oi' pressure. This indicator has been used in the prior art in conjunction with an amplifier and a cathode-ray tube to give a visual pattern of the pressure variations in the cylinder. The presence of knock is clearly indicated by the pattern on the cathode ray screen, but it is diiiicult to observe the intensity of the knock, and impossible in testing practice to measure its value. Knock intensity is best measured by my present invention.

In order to use a meter deflection to measure the intensity of the knock, it is necessary to remove the effect of valve-clatter which also sets up highfrequency vibration of the cylinder walls and electro-magnetic waves from the spark plug which generate static currents in the wires of the meter. Fortunately the valve clatter and ignition spark occur at different times than the detonation so that by an electronic switching action it is possible to remove the eiect of valve clatter and ignition spark. After removing the effects of valve clatter and spark, the question remains as to how the meter should be made to respond to the output of the indicator. The combustion cycles of the test engine are extremely variable. When tests are made by ear the presence of an audible knock once every thirty combustion cycles is considered to indicate knock. Observation of the cathode ray pattern showed that intermediate cycles might only indicate an intensity of ten per cent of the knocking cycle.

I may measure the time average knock intensity, or` a time average where the weight given to aknock of any given intensity is proportional to some suitable function of the knock intensity, and/or the time elapsed in each cycle.

For example, when using an averaging meter 38 shown in Figure 1, the meter deflection is made to average the knock intensity over a short period of time, giving the same weight to all knocks.

I preferably employ a meter 31 shown in Figure l which is designed to give an indication of the peak knock intensity. This has been accomplished by using a high speed critically damped meter in conjunction with an electronic circuit which would prolong the peak voltage due to knock just sufficient to make it easy to read the maximum meter deflection. This gives a meter which will follow the variations in knock intensity and clearly show the statistical fluctuations between combustion cycles. The sensitivity of the meter is adjusted so that a deflection in fthe middle of the scale corresponds to audible knock and with the action just described this deflection in effect corresponds to a calibrated ear.

'In Figure 1, a test engine 3 is provided with a pickup 4, preferably a pressure indicator pickup of the magneto-striction type manufactured by the Standard Oil Company of California. This pickup translates the pressure changes within the cylinder of the engine 3 to electrical energy by virtue of the change in the reluctance of a magnetic path caused by movement of a small diaphragm (not shown) in the cylinder wall, the voltage output being directly proportional to the rate of change in pressure. Internal combustion engines are almost always provided with poppet valves (see valve stem 5) and these poppet valves clatter in closing causing knock-type vibrations, and due to inertia of parts in the pickup 4 these spurious pressure change knock-type valve clatter vibrations are picked up too. The spark of ignition also sends out an electro-magnetic field which generates spurious pressure change currents in the pickup network of wires.

All the output of the pickup, regardless of its source is transmitted along a cable 6 to an amplier 8, and the shape of the wave transmitted along the cable 6 is shown roughly by a diagram 9 in which time is plotted in a horizontal direction (from left to right) and voltage in a vertical direction (above the line being positive and below the line nega-tive). (This wave is better seen in a diagram I0 after amplification.) As to be seen in the diagram I0, there is a train of small amplitude waves consisting of spurious pressure change waves which are really intake valve clatter II, ignition spark waves 'I and other vibrations it is not desired to finally indicate. then a high rate of pressure change wave I2 of large amplitude which is caused by the explosion of gas and resulting pressure rise and fall during the power stroke. On the crests of this pressure change wave are the minor pressure change variations I3 and I4 which indicate the presence and degree of knocking. Variations I5 are exhaust valve clatter during the closing of the exhaust valve. Y

The exact shape of 1, II, I3, I4, and I5 cannot be shown as 12,000 to 17,000 cycles per second would just be a blur using the scale employed in the drawings.

This wave train is amplified in its entirety in the amplifier 8 and is transmitted through a cable I6 to a tuned amplifier I'I. The shape of the amplified wave is shown by the diagram I0, all of these diagrams being similar to the diagram 9 as to time and voltage relations, each base line starting and ending at the same point in the engine cycle.

Cables B and I6 in combination with the ground form channels for the waves, and therefore the cables in Figure 1 can all be referred to as channels.

The same amplied Wave train I 0 is transmitted along a channel I8 to an integrator I9. The integrator integrates and modifies the wave train of the diagram I0 into a pulse of the general shape shown in a diagram 20 and this pulse is transmitted along a channel 2| to a clipper 22. The clipper 22 squares up the pulse into thesubstantially square pulse shown in a diagram 23. The degree of squareness can be varied to any extent considered necessary and the ignition wave 'Ieven if encroaching on slope I2 will be outside of the square pulse after clipping. This square pulse is transmitted from .the clipper 22 to rectifier and mixer 24 by a channel 25.

The tuned amplifier I1 preferably amplies the waves shown in the diagram I 0 that constitute a pass band of about 12,000 to 17,000 cycles per aereieeofsecond, This:amphfedrassbandJl is to; beA combined with, the square pulsesf, shown; in@ .the diagram/2.3 in the Vmixer. ,poniente dieiernaar and, mixer 24gand',istransmittedtomthe rectifier andrmixer by anl eleotro-magnetic.field' forming.. 5 y a. channel represented byrsparky symbols 28;

theY rectifier and Ifnixer;214 the wave ,trains 2.11m@ 23,218 combined to. form. thepwaveztrain.. shown, in*I a, diagram .4 29... This combined wave, trainris ,sentl .over a.v channel, to; a 4`network 3.1. 10 which', either-averages or. ,generatesA a .sustained peak voltage depending, onY the. position cina. switch .39..

The ^averager `or sustaine d peak voltage. gener atQl. operates..tostransmit a voltage'- over a; 15 challlolfzto av meter box.33.having the generalwave; form. of a.. diagram` 34.,.Ain. which, a rapidrise 3551s.? followed by a relativelyislow exponential decayi 3&1. Actually a compositewave is4 formed as aseries of thesewaves 3B; are superposed on each. 20 other at shortintervals.

Themeter ,box'33contains, two meters 31 and 38f.3r1..being a peak. voltage meter and Staan average; voltage. meter. A gang. switch composed ofv vanelectrically nonconductivecontrol rodv 3a 25 and single -pole l doublegthrow switchesLv 413,., 4 Il and 42, may beprovided to switch (by switch 10)v from the, meter 3,1 to'4 3,8. andto switch` (bysWitChes 4 i. andi-,42), the generator-'ll from.sustained. peak4 voltage.I generati onv for-the` meter; 3l; to. generation 3o of voltages proportional.. to: those` of, wave ,29s..for averaging by the nieterfli., Contacts .i3V totl, inclusive, are provided IOrtheSWitCheS...

Figure 2v4 shows1 a wiring diagram .Y of anl illustrative embodiment of my invention.

power supply means may be employedat for supplying the tubeswith the type `current they require. For illustration; show a trans-v former receiving house current at 5E,whaving` a core 51, coils58, 59 and 6B and avrectiiery Lbut 40 any otherpower supply can be employed justas welll inthe, pickup i, a grid leak 52 of 1.o meg. betweenwires Sand anda ground S3 for the wiref'l is provided. This grid leak and ground 45 coulolv be regarded as part of the` amplifier also, asthey control the grid of tube 64 and prevent excessive plate to cathode. currents,A the exact dividingline between elements having certain functions being of course vague, although the 50 elements and their functions are not vague. WhileI have shown certain dotted lines varound units in. Figure 2, it should be understood acertainV latitude. exists as to exactly what elements constitute. each unit. 5-

TheA amplifier 8 shows two triode tubes, S and 65, for. simiplicity but I may use a single double. triodetubein place of these vtwo tubes. The amplier 8f is shown as a conventional resistance coupled ampliiier. Any other type amplifier could be substituted,

The integrator I9 preferably contains a resistance. of about 0.5 meg. in series with a condenser 61 ofgabout .25 mfd.` By electric circuit theory the voltage between a wire 58 and the 65 groundis substantially the integral of the signal from'- the wire i8. Thisvoltage drop across the condenser n6l is impressed on a grid Wire 68 of a triode 69. Again I may usea singletube in place of triodes 69 and 10. Other circuits producing 70 similar integration may be used.

The. clipper 22 receives the output from the tube l69 which is controlledas to volume bya volumecontrol 1l, and senttotthe grid1 of a triode` Y with,y aV .5 meg.. resistance; 12 in the. gridccircuit which serves to clip the positive voltages` and` takegthe rounded-top olf: of wave, pulse 2U. A resistance 13 of `1.0 meg. and: a. double diode T4 -act as a Vfirst stage. voltage limiter and a resistance and a double diode 16 act as asecond stage. voltage limiter of` a conventional clipping circuit for the production ofy thev rectangularv wave pulses 23. I prefer to. take doubler triodesand make double diodes out of them` by wiring thek grids directly to the plates. Other clipping'circuits-may` be substituted. The numberof tubes is suchthat the phase of. the square pulse is positiveJ withrespectto the ground.

The tuned amplifier i l is conventional. I preferably employ a loosely coupled tuned, air core, or iron dust core, transformer as my band pass nlter composed preferably of primary coill 11 and secondary coil 18 and condensers 19 and 80. Any

other of the many band or high pass filters could be employed, Tube all is a part of the tuned amplier I1 with a rheostat 82V controlling its gain, and thereby controlling'theamplitude of the waves 2l.

The rectifier and mixer 2d could haver been shown as two units, one unit mixing and thel other unit acting as a modulated rectier. Because of the closerelation between them, they are shown as a single unit, but because of their separatev functions they may be claimed as two separatev units.

The mixer portion of the rectifier and mixer 2i. consists of a mixing tube 83 in which the voltages of the wave form 2l and' the'square wave form 23 are added algebraically. The amplitude of the wave 2l is controlled by the rheostat 5'2", the width of the wave 23 is controlled bythe rheostat il and the amplitude of the wave 23 is controlled by a rlieostat 313. The potential between the cable 25 and the ground follows the square pulse wave pattern 25, and makes the grid of the tube 83 more positive at intervals to cause more plate-to-cathode current in tube 83; and this square pulse current of the tube 33, in passing through coil I8 andcondenser El)y has the wave form 27 impressed on it from the primary coil l?. This combined wave train is vini'- pressed on the grid of a triode 85.

The rectier portion ofthe rectifier and mixer 2s consists of the triode' 85 which'V only transmitsk the more positive portion of the combined wave form. This is dueto a bias placed on the cathode of the rectifier tube 85 by a wire 8B. The wire 85 goes to a voltage divider 3l where the Bz-lat one end and a resistance 88 and o the ground at the other end are so disposed as that tube. So only the tops'of the square'wave 23 with wave 2l impressed lthereon are transmitted as wave 25- alongthe cables yStand ,52;

I may use a single envelope containing the two triodes Stand 85. While therectiiier and mixer.; portions of 24 are `closely tied'togetlier it is obvious that they have separateI functions;V and other mixers and/or' rectiiersl could be substituted.

The cable 52 transmitsithev wave 295.130 the cathode ray oscillograph tubeY 5-3- where it may be observed on screenA 54.

'Fh-'e @able@transmitting,Wars @Stagnation .1

10.45 Thisl triade. is .operated withoutv gridbiaslandf 3 I i A Vtively are in contact.

The generator 3i will first be described with the switch 39 to the left so that the contacts 46 and 4I; 48 and 42; and 50 and 40 respec- In this case the network 3| is a sustained peak voltage generator. Positive current of the wave form 23 runs from the cathode of the triode 85 through a plate 03 and a cathode 90 of a double diode tube 9i to charge a condenser 32. In the circuit shown in Figure 2 I have used a double triode connected. as diodes in order to obtain suiiicient conductance with the low cost radio receiver type tubes to rapidly charge condensers 92 and 95.

The condenser 92 is preferably of about 0.05 mfd. capacity and can therefore be charged in less than 0.001 of a second by the rectied signal Wave 29, so that the peak voltage on this condenser is closely proportional to the peak signal voltage of 29. As a resistance S3 of about 2.0 meg. is all that tends to short the condenser, the duration of the peak voltage on the condenser 92 is appreciably longer than the signal peak so that when the voltage of the condenser 82 is impressed through 3, lil, 40 on the grid of a triode 915, the resulting plate-to-cathode current in the tube is able to charge a condenser 95 of about 2.0 infd. capacity also shunted by a resistance 9B of about 2.0 meg. which condenser therefore has an increased time constant and maintains its peak voltage to control the grid of a triode 9i. The plate-to-cathode current of triode 91 makes the high speed peak meter 3? read the highest peak of the wave train 29 with a slow enough exponential decay of voltage between successive highest peaks so that the human eye can read the high value as the meter hand falls away slowly during the relatively slow discharge of condenser 05. A rheostat 93 provides a zero adjustment for the meter 3T.

When the generator 3l is used as an averager, the switch 38 is to the right so that the contacts 4I and 4l; 42 and 49; and 40 and 5I are in contact. Then the voltage of the small condenser 92 is applied to the grid of the triode 9'? and the plate-to-cathode current of triode si makes the high speed averaging meter 3s read the average of the peaks of the wave train 2S for the last few seconds as they appear across condenser 92 and resistor 93. To this end, the

meter 33 is shunted by an integrating condenser 99, the integrating effect being regulated by a variable resistor in series with the meter.

Operation The pickup 4 picks up the wave 9 which ine cludes the valve clatter, ignition spark electromagnetic Waves, and the rate of pressure change valves including the high frequency rate of pressure change waves. These are all sent to the amplifier which amplies them all in a linear manner.

It will be seen that the output I0 of amplifier 8 is proportional to the rate of change of pressure I2, which includes the high frequency oscillations I3 and I4 due to knock, 'I due to spark ignition and II and I due to valve clatter. This voltage I0 is impressed on an integrating circuit I9 which by the mathematical process of integration (performed electrically, of course) integrates the rate of change of pressure plotted against time of I0 into the pressure plotted against time of 20. The Y ure 2) in the averager or sustained peak voltage generator so that it is operative only during the interval when considerable pressure exists in the cylinder. This operation removes the voltages I due to ignition spark and II and I5 due to valve clatter since these voltages appear only when the pressure is low. The parallel channel I6, 28 with the band pass lter 11, 78 in the tuned amplifier II removes all the voltages from I0 except 21 which are those corresponding to the excitation of high frequency modes of vibration in the interval between 12,000 and 17,000 cycles per second. The waves 2l areonly measured at times when the cylinder pressure is high due to the bias 88 on rectifier 85 and this eliminates the valve clatter, the spark waves and other disturbances occurring whenthe pressure is lower. Then a. function of the peak voltages or the sustained peak voltage of the measured portion of 21 is produced in wave 34 generated in generator 3|, depending on the position of the switch 39. When 39 is to the left, sustained peak voltage is generated and measured; when it is to the right, peak voltages are generated and the average thereof is measured. This voltage wave 34 that is measured has exponential decay 36 but in a short interval is replaced by a new wave. Meter 31 thus indicates the peak, or largest knock in the last few seconds, when it is connected. When meter 38 is connected, it indicates the average knocking of the last few seconds.

As pointed out above many changes of circuits following the standard circuits old in the art, and many substitutions of dierent tubes, conventional eleinents or units havingrthe same function, may be done by those skilled in the art without involving invention, the scope of my invention being set forth in the following claims.

Having described my invention, I claim:

l. A detonation meter for indicating the intensity of knocking in a cylinder of an internal combustion engine comprising, in combination, a pickup for converting pressure variations within a cylinder into electrical voltages representative thereof, said voltages including a low frequency component representative of the main pressure wave in said cylinder, and high frequency components representative of knocking, a dual channel network fed by said pickup, the first channel including an integrating circuit for converting said low frequency component into waves of generally square wave form, and a clipping circuit to square up the output of the integrating circuit. said second channel including a filter for substantially eliminating said low frequency component to provide a voltage consisting essentially of said high frequency component, a mixing circuit for adding the square wave voltages to the filtered voltages to produce a resultant voltage, a threshold tube for eliminating components of said resultant voltage which are Vof less than a predetermined amplitude, a diode rectier tube having an anode and a cathode, means for feeding the output of said threshold tube to the anode of said rectifier tube, a fixed resistance having one terminal thereof connected to said cathode and the other terminal thereof grounded, a condenser connected in parallel with said xed resistance to form a pulse-generating circuit, an output tube having an anode, a cathode and a control grid, means for supplying operating potentials to the electrodes of said tube, a lead connecting the cathode of said rectifier tube to the control grid of said output tube, a second fixed resistance having oneV terminal thereof connected to the catliode of said output tube, and a two branch circuit connected between the other terminal of said second xed resistance and ground, one branch including a fixed resistance and a variable resistance connected in series, and the other branch including a xed resistance and a meter circuit connected in series therewith, and a fixed resistance connecting the junction between said meter circuit and said-'.last-mentioned xed resistance to a positive power supply terminal, said meter circuit including an ammeter, a variable resistance connected in series with said ammeter, and an integrating condenser connected in parallel with the variable resistance-ammeter combination.

2. A detonation meter for indicating the intensity of knocking in an internal combustion engine cylinder comprising, in combination, a pickup for converting pressure variations in a cylinder into electrical voltages representative thereof, means for amplifying said voltages, a parallel channel network for the amplified voltages, one channel including an integrator and a clipper to convert said voltages into square waves, said second channel including a, filter tuned to a frequency band of from 12,000 to 17,000 cycles per second, a mixing circuit to add .the square waves to the filtered voltages, a biased tube for eliminating components of less than a predetermined magnitude in the output of the mixing circuit, a diode rectifier tube having an anode and a cathode, means for feeding the output of said biased tube to the anode of said rectier tube, a xed 'resistance having one `terminal thereof connected to said cathode and the other terminal thereof grounded, a condenser connected in parallel with said fixed resistance to form a pulsegenerating circuit, an output tube having ananode, a cathode and a control grid, means for supplying operating potentials to .the electrodes of said tube, a lead connecting the cathode of said rectier tube to the control grid of said output tube, a second fixed resistance having one terminal thereof connected to the cathode of said output tube, and a two branch circuit connected between the other terminal of said second fixed resistance and ground, one branch including a xed resistance and a variable resistance connected in series, and the other branch including a xed resistance and a meter circuit connected in series therewith, and a xed resistance connecting the junction between said meter circuit and said last-mentioned fixed resistance to a positive power supply terminal, said meter circuit including an ammeter, a variable resistance connected in series with said ammeter, and an integrating condenser connected in parallel with the variable resistance-meter combination.

RAYMOND G. PIETY.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS 

